1. Field of the Invention
The present invention relates to an offset canceller for canceling the offset in a signal output. More particularly, the present invention relates to an offset canceller applicable to an output circuit of a liquid crystal display device driver having a plurality of output operational amplifiers, as an example.
2. Description of the Background Art
An integrated circuit for driving a liquid crystal display (LCD) device, for example, includes a plural number of output operational amplifiers. In canceling the offset of those operational amplifiers, the routine practice is to cancel only the offset voltage, as disclosed in, for example, U.S. Pat. Nos. 6,946,905 B2, 6,448,836 B2 and 6,930,529 B2 to Kokubun et al., Kokubun et al., and Tobita, respectively.
However, if a capacitive or resistance device for setting the amplification factor is connected externally of the operational amplifiers, it is necessary to correct the offset, ascribable to the capacitance or resistance, with respect to the amplification factor. To such a case, the conventional offset canceller circuitry cannot be applicable.
Moreover, the conventional method for compensating for the offset suffers from the problem that no signal can be output during the operation of the offset compensation.